{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"17d0427cfd110dac67a19de334878a03693c9a7d19f2b903914a31de8caf0c2c","created":"2026-10-03T07:18:02Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"ce610c172617941f286ede1767979f79c9a2be4283b83516a9b4d73b97d05a47","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"earth.geodynamo.hadean-dynamo","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"Tiny crystals called zircons from the Jack Hills of Australia, some older than 4 billion years, contain magnetic grains that may record an ancient field. Researchers disagree on whether the magnetization formed with the crystals or was added much later.","posed_since":"2015","precise":"Paleointensities from Jack Hills detrital zircons (Tarduno and coauthors, Science 2015, https://doi.org/10.1126/science.aaa9114) suggest a geodynamo from about $4.2\\,\\mathrm{Ga}$ with strength comparable to today's, whereas Borlina and coauthors (Science Advances 2020, https://doi.org/10.1126/sciadv.aav9634) argued that the magnetic carriers are secondary and the record unreliable. Determine whether a geodynamo existed between about $4.2 \\text{ and } 3.5\\,\\mathrm{Ga}$, and its intensity. An answer is a primary paleointensity record older than $3.5\\,\\mathrm{Ga}$ whose magnetic carriers are shown by in situ dating and micromagnetic imaging to be as old as the host crystal.","problem_ref":null,"references":"","settled_by":"Paleomagnetic measurements on Hadean and Eoarchean zircons whose magnetic inclusions are demonstrated to be primary.","status_note":"Tarduno and coauthors defended a primary record (PNAS 2020, https://doi.org/10.1073/pnas.1916553117) against Borlina and coauthors 2020; no decisive test was found in a 2026 literature check.","title":"Did Earth have a magnetic field 4.2 billion years 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